1. Technical Field
The present invention relates to the unloading of fluid-like or flowable cargo in a container lined with a container liner. In particular, it relates to a container liner with displacement means for moving the contents of the liner towards a discharge opening in the liner.
2. Background Art
Bulk cargo containers are used for transportation of a variety of products. For some products, it is advantageous to fit the container with a flexible liner of e.g. polyethylene or the like. Powered, granular or other flowable materials can be loaded directly from a storage space, such as a silo or the like and into the liner of the container saving a packaging operation by the manufacturer while also making more efficient use of the container space, as packaging materials, such as bags, pallets, etc. do not have to be transported with the products.
The product in the container can subsequently be unloaded and transferred directly into a new storage space with tie recipient. All in all, the whole handling process is considerably easier and a lot less expensive. The product can be discharged from the container liner by tilting the container whereby the powdered, granular or similarly flowable material flows under gravity towards and out of a discharge open at the lower end of the container liner.
However, some of the powdered or granular material is usually trapped in the lower corner regions of the container. In order to move the powdered material towards the discharge, it is known to mount triangular corners, to minimise the likelihood of products accumulating in the corner regions during the discharge operation. An example of such rigid angled corners integrated in a bulkhead is known from U.S. Pat. No. 4,799,607. From U.S. Pat No. 5,531,361, an active bulkhead is known where tetrahedron-shaped inflatable bags are mounted in the lower corners on each side of the discharge. Similarly, inflatable tetrahedrons mounted inside the container liner are known from U.S. Pat. No. 5,489,037.
From international patent application No. WO 95/01925, another solution is known. Here, two inflatable bladders are provided at each lower corner region at the discharge end of the liner.
By these known solutions, the material in the corner regions of the liner is lifted up in the corner region whereby the angle of dip of the material might be exceeded causing the material to slide towards the centre of the container liner. The size of the inflatable corners are relatively restricted due to the design of the corners. Moreover, the lifting of the material in the corners by inflating the corners produces an immense stress in the walls of the corners as well as the walls of the liner itself. This stress is caused by the air pressure in the inflated corner deriving from the pressurised air source filling the corner as well as the load of the material being lifted. This means that the material in the liner just outside the area exposed to impact by the inflating liner could form a dip in the liner creating stress in the liner wall as well.
Such stress can cause the corners or even the liner itself to burst which is unfortunate for obvious reasons as the material is thereby wasted with all the distressing implications associated therewith.
In the above mentioned U.S. Pat. No. 5,531,361, a vibrating mechanism is installed for vibration of the rigid support surface of the corner lifting the liner corner. Hereby, the flow of the material is eased and the discharge flow is enhanced.
However such bulkhead designs take up a lot of space in the container whereby the space for storing the products to be transported is reduced.
It is the object of the invention to provide an improved liner and a method of discharging said liner in such a manner that the above-mentioned drawbacks with the existing liners on the market are avoided.
This object is achieved by the present invention consisting of a liner for use in a box-like cargo container for transportation of powder, granular or other flowable products, said liner comprising top and bottom walls, two side walls and first and second end wall portions corresponding to the wall portions of the container, a discharge opening at the lower portion of said first end wall, through which the contents of the liner are discharged, displacement means for guiding the content of material towards said discharge opening, said displacement means comprising at least one inflatable, flexible bag having an essentially triangular or trapezoid shape substantively abutting said end first wall, and a first essentially triangular portion supporting the outside surface of the floor and a second essentially triangular portion supporting the adjacent side wall portion of the liner, said triangular bag comprising three corners positioned substantively at the edge of the end wall and the side wall portion, the end wall and the bottom wall portion, and the side wall and the bottom wall portion
By the present invention, an inflatable bag is provided that moves the material in the liner sideways towards said discharge opening. An inflatable bag according to the invention has an essentially triangular shape and is aligned with the end wall and is attached to the liner along the edge of the side wall and the floor of the liner. This means that the material is not lifted but pushed sideways away from the side wall of the corner region of the container. The stress implied in the bag as well as in the liner is thereby reduced considerably.
In particular, the upper corner portion of the flexible bag is provided with a flexible inflation tube for inflation of the flexible bag with pressurised air causing the inflation to advance from the upper portion and downwards in the bag as the amount of material in the liner is reduced. This means that the pressurised air in the flexible bag distributes itself in the correct manner causing the material to xe2x80x9crollxe2x80x9d. The upper portion of the material trapped in the corners at any given time is pushed sideways by the progressing inflation of the bag whereby the angle of dip is exceeded and the material slides down towards the discharge opening. The method and design of the liner relieve the material from excessive stress thus eliminating the risk of overloading and bursting the bags and/or the liner itself during the discharge operation.
In addition, the discharge operation is more efficient since the bags can be designed in considerably larger dimensions without increasing the risk of causing the bag to burst due to excessive internal pressure.
Moreover, by attaching the triangular flexible bags to the outside surface of the liner by a number of individual double adhesive strips, the liner occupies a minimum of space when folded together and shipped off to the point of use. Also, a liner with flexible corner bags according to the invention can be manufactured in a simple and inexpensive manner. The points of attachment can be chosen in accordance with the desired impact of the inflated bag on the corner region of the liner.
In a preferred embodiment, the inflatable bag comprises two essentially triangular or trapezoid, flexible sheets secured to each other in a gas-tight manner along the edges forming an interior space that can be increased in volume by inflation with pressurised air. Hereby, the manufacture of the flexible inflatable bags is simple and the production is easily altered to accommodate different sizes of bags. Moreover, the bags hardly occupy any space when deflated.
In the preferred embodiment, two flexible sheets are of an elastomeric material, preferably polyethylene, polypropylene or the like, said sheets being secured to each other by welding. The inflation tube comprises a first end that is preferably welded to the upper corner portion of the sheets forming the bag, said sheets being provided with a non-adhesive paper sheet prior to their assembly, such as a heat-transporting grease-proof paper sheet, said paper sheet being positioned in the opening of said first end of the inflation tube. The inflation tube is of a tubular plastic material or a similar or of somewhat lighter material than the sheet material of the bags. By this embodiment, the entire welding of the edges can be performed in a plane state and optionally also in a single operation depending on the welding equipment. The paper sheet at the end of the inflation tube prevents closure of the corner towards the interior of the bag. At the same time, the paper sheet only occupies an area inside the tube end. This ensures a gas-tight sealing of the corner region of the bag around the inflation tube. When initial pressurised air is advanced through the inflation tube, the small paper sheet is blown into the interior of the bag and is thus no obstacle to the inflation operation.
In a preferred embodiment, the sheets of the flexible bag are of a stronger sheet material than the sheet material of the liner. This is advantageous, in particular with the larger sized flexible inflation bags, as the bags are capable of resisting a large amount internal air pressure. It must be noted that by the term air pressure, it is realised by the invention that any other gas than air can be used for the inflation.
In a preferred embodiment of the invention, the flexible bag has a height of approx. 40 inches (100 cm), a width of about 44 inches (110 cm) and a length which is at least equal to the height, preferably at least two times the height, and between 80 to 120 inches (200 to 300 cm). A standardised bulk cargo container is 8 feet wide and when using two flexible inflation bags, an efficient funnel-like chute leading towards the discharge opening (which typically is about 12xe2x80x3 in diameter) can be formed in the floor of the container. The length of the flexible bag can be regulated according to the characteristics of the product to be stored in the container liner and the discharge operation procedure. In particular, by regulating the length and maintaining the height on the flexible bag, the angle of the upper edge can be regulated. The preferred length depends on the tilting angle of the container and the angle of dip of the material. For some granular materials, this angle of xe2x80x9cself-slidexe2x80x9d is very low and for other granular materials, the angle is high. The steeper the angle the smaller the required relative difference between the height and the length of the flexible bag.
In the preferred embodiment of the invention, the displacement means comprise two inflatable, flexible bags at each lower corner region of the first end wall on each side of the discharge opening in order to create a funnel-like shape of the discharge region of the liner.
In one preferred embodiment, the triangular flexible bags are of the same size. This is particularly advantageous when the discharge opening is at the centre of the liner. In an alternative embodiment, the triangular flexible bags are of different sizes so that the flexible bag in the left corner region is larger than the right bag when viewed from the outside. The discharge opening is preferably set off from the centre line of the container liner and is advantageously placed in the right hand side, since it is usually the right-hand door of the two doors of a standard container that opens first. By using two inflatable bags of different sizes, a funnel-like shape can be provided for an off-set discharge opening. An off-set discharge opening can be advantageous, as the discharge of the contents of the liner is possible by opening the right-hand door only. In order to facilitate the discharge operation, the largest inflatable bag is provided with an inflation tube of approx. 30xe2x80x3 (150 cm) in length. Hereby, the inflation tube of the left bag which is hidden behind the closed left-hand door is accessible and the left corner flexible bag can be inflated without having to open the left door.